Balkh is a town in the Balkh Province of Afghanistan. It is located approximately 20 kilometres (12 mi) to the northwest of the provincial capital city Mazar-i-Sharif and approximately 74 kilometres (46 mi) to the south of the Amu Darya and the Afghanistan–Uzbekistan border. In 2021–2022, the National Statistics and Information Authority reported that the town had 138,594 residents. Listed as the eighth largest settlement in the country, unofficial 2024 estimates set its population at around 114,883 people.

Historically, the site of present-day Balkh was held in considerably high regard due to its religious and political significance in Ariana. A hub of Zoroastrianism and Buddhism, the ancient city was also known to the Persians as Zariaspa and to the Greeks as Bactra, giving its name to Bactria. As such, it was famously known as the capital of Bactria or Tokharistan. The Italian explorer and writer Marco Polo described Balkh as "a noble city and a great seat of learning" prior to the Mongol conquests. Most of the town now consists of ruined buildings, situated some 12 kilometres (7.5 mi) from the right bank of the seasonally flowing Balkh River, at an elevation of about 365 metres (1,198 ft).

While it is one of Afghanistan's ethnically diverse settlements, Tajiks account for the majority of Balkh's populace and have continuously inhabited the site for millennia. The main language of the town is Dari, which is spoken by a significant majority. Balkh's surrounding region is particularly known for its archeological sites, which attest the presence of many different civilizations that influenced the town's society in various eras. The Belgian-French explorer and spiritualist Alexandra David-Néel associated Balkh with Shambhala, a mythical kingdom that features prominently in ancient Tibetan Buddhism, and also offered the Persian Sham-i-Bala (lit. 'elevated candle') as an etymology of its name. In a similar vein, the British author John G. Bennett, whose academic focus was on the teachings of the Armenian-Greek mystic George Gurdjieff, speculated in his works that Shambhala may have been a Bactrian Sun temple called Shams-i-Balkh, taking note of the Afghan author and mystic Idries Shah as the source of this suggestion.

The origin of the name Balkh is unknown. Wilhelm Eilers proposed that the region was named after the Balkh River (in Greek transliteration Βάκτρος, i.e. Baktros) from underlying Bāxtri-, itself meaning 'she who divides', etymologically from the Proto-Indo-European root *bhag- 'to divide' (whence also Avestan bag- and Old Indic bháj-).

The Bactrian language name of the city was βαχλο, i.e. Bakhlo. In Middle Persian texts, it was named Baxl, i.e. Bakhl (Middle Persian: 𐭡𐭠𐭧𐭫). The name of the province or country also appears in the Old Persian inscriptions (B.h.i 16; Dar Pers e.16; Nr. a.23) as Bāxtri, i.e. Bakhtri (Old Persian: 𐎲𐎠𐎧𐎫𐎼𐎡𐏁). It is written in the Avesta as Bāxδi (Avestan: 𐬠𐬁𐬑𐬜𐬌‎) . From this came the intermediate form Bāxli, Sanskrit Bahlīka (also Balhika) for "Bactrian", and by transposition the modern Persian Balx, i.e. Balkh, and Armenian Bahl. This same root entered the Greek language as Baktra (Ancient Greek: Βάκτρα), often written in the form Bactra.

An earlier name for Balkh or a term for part of the city was Zariaspa (Ancient Greek: Ζαρίασπα), which may derive from the important Zoroastrian fire temple Azar-i-Asp or from a Median name *Ζaryāspa- meaning "having gold-coloured horses".

The nickname of Balkh is "the Mother of All Cities".

The first historical reference for Balkh is found in the Mahabharata, where it is called 'Valhika' through which an important trade route passed. The same source mentions that the place is famous for good breed of mules. Also the place was found with people who traded in Chinese silk, pashmina, jewels and perfumes.^{[full citation needed]}